The present invention relates generally to an optical system, and more particularly to an optical system for panoramic cameras, panoramic projectors or the like, which is compact in size with high resolving power, and adapted to form full-360° angle-of-view images from the surrounding scene on an image plane or project images located on the image plane onto the full-360° angles of view.
For prior art optical systems adapted to obtain full-360° angle-of-view images from the surrounding scene using a catoptric system, there are such catoptric systems as set forth in Patent Publications 1, 2 and 3 known in the art, which are each built up of a front unit comprising a transparent medium that is rotationally symmetric about a center axis and has two internal reflective surfaces and two transmissive surfaces, and a rear unit that is rotationally symmetric about the center axis and has a positive power.
Patent Publication 1
U.S. Pat. No. 4,566,763
Patent Publication 2
U.S. Pat. No. 5,473,474
Patent Publication 3
U.S. Pat. No. 6,611,282
However, a problem common to the aforesaid prior art optical systems is that when the surrounding scene is taken with the optical system lying toward the zenith, images go worse because an entrance pupil in a section including the center axis is located at or near the center axis; the effective diameter of the entrance surface of the optical system grows large, giving rise to the incidence on the optical system of a lot more harmful flare light from the zenithal direction.